Database overview

    When using any of the data presented below, please be sure to acknowledge the MGC team by citing Papers I, V and X for the imaging, spectroscopy and bulge/disk decomposition respectively, and by using this acknowledgment.

    The public MGC database contains the full MGC imaging data, various ASCII catalogues, an individual multi-extension object fits file for each object in MGC-BRIGHT (BMGC < 20 mag) as well as a number of files containing the parameters of the MGC imaging survey. The data obtained for MGCz, the MGC redshift survey which complements pre-existing, publicly available spectroscopy to provide redshifts for the full MGC-BRIGHT sample, are distributed as part of the object fits files. These also include said public data.
     

    ASCII catalogues

    Here we offer a number of catalogues as plain ASCII files. Each catalogue contains one line per object with multiple white-space separated columns. The .par files give short explanations of the columns in the corresponding catalogue files. The various numerical codes, used e.g. for object classification, are explained here. Some of these catalogues are gzipped because they are very large.
    Base catalogues:
    These were derived from the MGC imaging data. They are essentially the output of SExtractor.
    mgc_bright (.par) All objects with BMGC < 20 mag (corrected for dust extinction, MGC-BRIGHT). To obtain a clean galaxy catalogue, select all objects with CLASS=1, INEXR=0 and QUALITY<=2.
    mgc_faint_master.gz
    (.par)    		 All objects with BMGC >= 20 mag (corrected for dust extinction). Objects with B > Blim are not classified. The only classes used here are 1, 8, 14 and 15.
    mgc_faint.gz (.par) A "cleaned" version of mgc_faint_master (MGC-FAINT): all objects from mgc_faint_master that do not lie in exclusion regions (using a safety buffer of 50 pixel), do not lie in MGC fields 14, 15 or 65 (which are of sub-standard quality) and have B < Blim. Use this for science, not the one above.
     
    Matched catalogues:
    These were derived by matching MGC stars and galaxies with BMGC < 22 mag to catalogues from other sources as indicated. For each matched object the catalogues contain both the MGC information (from the base cats) as well as the information from the other source, separated by the distance in arcsec between the two catalogue positions.
    mgc_sdss.gz (.par) All SDSS-DR1 objects with g < 21 mag (from PhotoPrimary "outer joined" with SpecObj). Information derived from SDSS spectroscopic observations is included where available. This will be upgraded to the final DR when available.
    mgc_2dfgrs (.par) The photometric input catalogue of the 2dFGRS NGP strip (description). Hence this catalogue contains no spectroscopic information.
    mgc_2qz (.par) The combined 2QZ/6QZ catalogue (description).
     
    Full catalogues:
    These were generated from the individual object fits files (see below) and hence only contain objects with BMGC < 20 mag. They are probably the most useful for the average user because they contain all the information available from the various sources. If you require any of the parameters that are included in the fits files, but not in the catalogues below, then please contact us and we will be happy to help.
    mgc_zcat (.par) Contains the most useful bits of information for each object from each of the various sources.
     
    Structural catalogues:
    These were derived from 2D surface brightness profile fitting of MGC-BRIGHT galaxies using GIM2D. The details of this process are described in Paper X which is pretty much a must-read before you will be able to sensibly use any of these catalogues. Since they are a recent addition to the database the information contained in them is not yet included in the object fits files (see below) or in any other catalogues. Please note also that the structural catalogues are a little rough around the edges (e.g. some columns are duplicated).
    The following are the raw GIM2D output catalogues:
    gim2d_sersic0.70 (.par) Single component fit: Sersic profile, where the ellipticity is restricted to be < 0.7.
    gim2d_sersic0.92 (.par) Single component fit: Sersic profile, where the ellipticity is restricted to be < 0.92 (corresponding to an inclination of 85 deg).
    gim2d_dv_exp (.par) Two component fit: de Vaucouleurs + exponential profiles.
    gim2d_sersic_exp (.par) Two component fit: Sersic + exponential profiles.
    In the following catalogues we have combined the GIM2D output above with the extraction and redshift catalogues. These also contain other useful parameters such as k-corrections, spectral types, etc, as well as pre-computed intrinsic parameters such as absolute magnitudes (using ΩM = 0.3, ΩΛ = 0.7 and H0 = 100 km/s/Mpc).
    mgc_gim2d_sersic0.70 (.par) Single component fit: Sersic profile, where the ellipticity is restricted to be < 0.7.
    mgc_gim2d_sersic0.92 (.par) Single component fit: Sersic profile, where the ellipticity is restricted to be < 0.92 (corresponding to an inclination of 85 deg).
    mgc_gim2d_dv_exp (.par) Two component fit: de Vaucouleurs + exponential profiles.
    mgc_gim2d_sersic_exp (.par) Two component fit: Sersic + exponential profiles.
    mgc_gim2d (.par) In this catalogue we have replaced the two component Sersic + exponential fit with a single component Sersic fit in cases where the two component fit was deemed unphysical. This process ("logical filtering") is described in detail in Paper X. We believe this catalogue provides the most meaningful structural decomposition and we use this for our science.
     
    Other catalogues:
    Any that don't fit into the above categories.
    mgc_cc_bright (.par)
    mgc_cc_faint (.par)    		 Catalogues of `primary' galaxies and their dynamically close companions as used in Paper VI. `bright' and `faint' in this case refers to the -22 < MB < -19 and -21 < MB < -18 mag samples of that paper respectively. Each catalogue entry contains data for two galaxies: the `primary' galaxy first and the companion second. Hence a pair consisting of galaxies A and B will usually be listed twice: once as A,B and once as B,A. Galaxies may have multiple entries as either primary or companion.
    mgc_pca (.par) Catalogue of galaxies as used in Paper VII.
    mgc_mc (.par) Catalogue of misclassified compact galaxies as used in Paper IX (Table 3).
    mgc_asym (.par) Catalogue of asymmetry measurements as used in Paper XV.
    pm2gc_tables.tar.gz Tarball containing the tables of the PM2GC paper.
    pm2gc_superdense.txt Catalogue of superdense galaxies as used in this paper (Table 5).
    pm2gc_gf_morph.txt Catalogue of morphological classifications of the PM2GC general field sample as used in this paper (Table 7).

     

    Object fits files

    We have produced a separate multi-extension fits file for each object in MGC-BRIGHT (ie. BMGC < 20 mag, see above), in which we collate all the available information for that object, including in particular the MGCz spectroscopy. The naming convention for these files is MGCnnnnnB.fit.gz where nnnnn is the MGC ID (column 1 in all the ASCII catalogues). Each of the fits extensions contains information from a different source. This information can be data (a fully reduced image or spectrum) and/or measurements derived from that data. The latter is stored in the extension's fits header along with observational info where appropriate. In all we have used data from the following sources:

    • MGC
    • SDSS-DR1 imaging
    • MGCz
    • SDSS-DR1 spectroscopy (and catalogue data)
    • 2dFGRS
    • 2QZ
    • NED (excluding SDSS, 2dFGRS and 2QZ objects)
    • PF (P.J. Francis et al., 2004, AJ, 127, 646)
    • LSBG (C.D. Impey et al., 1996, ApJS, 105, 209)

    The primary data unit contains the MGC postage stamp and may be followed by zero, one or more extensions depending on how much additional information is available for this object. Extensions are added in the order of the surveys as they are listed above. A given object may receive zero, one or more extensions from a given survey, depending on the number of observations of that object in that survey. For example, most galaxies have no matches in the 2QZ and hence no 2QZ extension is added for these objects. On the other hand, many galaxies were observed more than once by MGCz and each observation is contained in a separate fits extension, which are ordered by quality. Also, more than one object from, say, NED may be matched to the same MGC object. Again, each of the "observations" (ie. NED objects) are contained in separate extensions, this time ordered by distance from the MGC object.

    The above implies that information from a given survey is not always found in the same extension. So a command like "splot MGC03322B.fit[3]" in IRAF, which accesses the third fits extension, will not necessarily show you the spectrum you were after. However, many softwares that handle fits files make use of the extended filename syntax which allows you to address an extension by its name and version number, ie. by the values of the EXTNAME and EXTVER keywords. In our case EXTNAME is set to either IMAGE, SPECTRUM or OBJECT_DATA depending on whether the extension contains a data unit or just a header. EXTVER numerically encodes the surveys. For example, to view the (first) 2dFGRS spectrum for MGC03322 in IRAF, simply use "splot MGC03322B.fit[SPECTRUM,3]", whereas the SDSS r-band postage stamp could be viewed with "ds9 MGC03322B.fit[IMAGE,2]" (or simply "ds9 MGC03322B.fit[IMAGE]" since there are no other extensions with the name IMAGE).

    We have attempted to homogenise the information provided by the various surveys by using the same keywords in each extension whenever possible. We also provide translations of all object classification and redshift quality parameters to the MGC system.

    Below we descibe in more detail the extensions produced by the various surveys. The numerical codes used in the catalogue data included in the headers are explained here .

    MGC    extension code, example header
    The primary data unit (or zeroth extension) contains a postage stamp cut from the MGC imaging data around the position of the object. It is oriented in the usual way (North up, East left). The header contains information on the observation as well as most of the catalogue data for that object from mgc_bright.

    SDSS imaging    extension code, example header
    This extension contains a postage stamp cut from the SDSS-DR1 r-band data around the MGC object position. The header contains some observational information taken from the SDSS images. It does not contain any information about any SDSS objects that may or may not have been matched to the MGC object. This extension will be present even when no SDSS objects were matched to the MGC object. Consequently, this extension exists for nearly all objects. The only exceptions are 33 MGC objects which lie in a "hole" in the SDSS imaging data.

    MGCz    extension code, example header
    This extension always contains a spectrum. Most of the spectra were observed with AAT/2dF but additional observations were obtained with Gemini/GMOS, NTT/EMMI, TNG/DOLORES and ANU 2.3m/DBS. The header contains observational information as well as some measurements derived from the data. There may be multiple observations and hence multiple MGCz extensions, in which case they are ordered by the quality of the spectrum.

    SDSS    extension code, example header
    The header of this extension always contains the SDSS photometric catalogue data. If spectroscopic observations for this SDSS object are available then the header also contains the observational information as well as the spectroscopic catalogue data, while the data unit of course contains the spectrum itself. There is only one observation (and hence only one extension) for each SDSS object. However, multiple SDSS objects may be matched to the same MGC object, in which case they will be ordered by distance from the MGC object.

    2dFGRS    extension code, example header
    The header of this extension always contains the data from the photometric input catalogue. If spectroscopic observations for this 2dFGRS object are available then the header also contains the observational information as well as the spectroscopic catalogue data, while the data unit of course contains the spectrum itself. A given 2dFGRS object may have multiple observations and/or more than one 2dFGRS object may be matched to the same MGC object. In either case the extensions are ordered by spectral quality.

    2QZ    extension code, example header
    The header of this extension always contains the data from the photometric input catalogue. If spectroscopic observations for this 2QZ object are available then the header also contains the observational information as well as the spectroscopic catalogue data, while the data unit of course contains the spectrum itself. A given 2QZ object may have up to two observations, which are ordered by spectral quality.

    NED    extension code, example header
    This extension never has a data unit. The header contains NED catalogue data. More than one NED objects may be matched to the same MGC object, in which case the extensions will be ordered by distance from the MGC object.

    PF    extension code, example header
    This extension never has a data unit. The header contains PF catalogue data.

    LSBG    extension code, example header
    This extension never has a data unit. The header contains LSBG catalogue data.
     

    MGC survey parameter files

    The files below describe various aspects of the MGC imaging survey. Various bits of C code in connection with these files are available on request. They might be useful e.g. when calculating the area of some sub-region.
    exregions Contains all exclusion regions. The exclusion regions are due to CCD edges, the vignetted corner of CCD 3, CCD defects, satellite trails, bright stars and galaxies (B < 12.5), diffraction spikes and a few unintentional overlaps between CCDs 2 and 3 of neighbouring fields. In addition, CCDs 3 and 4 of field 79 are entirely covered by exclusion regions because these images were not read out properly. Exclusion regions are either rectangular or ellipsoidal and are defined by the position of their centre (MGC field, CCD and x,y coordinate), their width or semi-major axis, height or semi-minor axis and their angle with the image x-axis.
    flims RA limits of MGC fields in degree. These define the boundaries between neighbouring and overlapping fields (recall the survey geometry). These do NOT apply to CCD 3. In several cases the upper RA limit of a field is slightly smaller (by up to 0.7 pixel) than the lower RA limit of the next field. This is due to a minor mistake during the extraction process.
    area_50 Active survey area of each MGC field and CCD, ie. those pixels that lie outside exclusion regions and between the RA limits (not CCD 3). Growable exclusion regions were enlarged by a safety buffer of 50 pixel. The total survey area is the sum of the last column.
    area_noexr Full survey area, ignoring all exclusion regions (but not the RA limits).
    seeing Seeing of each MGC field in arcsec.
    zeropoints Magnitude zeropoints for each MGC field.
    compllims Point source completeness limits for each MGC field, raw and extinction corrected.

     

    Access

    Unfortunately, we don't have a nifty web interface for easy access to the object fits files or the full MGC imaging data (everything else is available above). The most convenient way for you to access these data is to request the DVD version of this database from us. In fact, due to space limitations the original imaging data is only available on the DVDs. The original imaging data are stored on DVDs II and III while the object fits files are on DVD I in the directory data/pstamps/.

    For the object fits files you have the alternative of dowloading them directly from http://www.hs.uni-hamburg.de/jliske/mgc/data/pstamps/. The naming convention for these files is MGCnnnnnB.fit.gz where nnnnn is the MGC ID (column 1 in mgc_bright). The idea is to select the objects you're interested in from one of the ASCII catalogues above (e.g. using awk) and then use a utility like wget to download their object fits files. The csh script mgcgetobjfits.csh can help you with this. It takes an ASCII catalogue as input, generates the appropriate wget command from it and then executes it.

    Example: you want to look at the spectra of all galaxies brighter than 19th magnitude which have a good quality redshift and for which more than one spectrum is available.

    First select out the above objects from mgc_zcat using:

    >> awk '$19 == 1 && $15 < 19.0 && $123 >= 3 && $123 <= 5 && $124 >= 2 {print}' mgc_zcat > gals_mult_spec

    Remember that the columns of mgc_zcat are explained in mgc_zcat.par and the numerical codes are explained here.

    Now retrieve the object fits files for these objects using:

    >> mgcgetobjfits.csh gals_mult_spec fits_files

    which places the files in the directory fits_files. Use

    >> mgcgetobjfits.csh --help

    as a reminder of the syntax.

    WARNING: use mgcgetobjfits.csh at your own risk. It is not very clever, does virtually no error-trapping and is certainly not fool-proof. Worst of all it is pretty slow. Depending on your internet connection and the size of your sample it may take many hours to download the requested files. For example, a transfer to the RSAA takes about 1.5 sec per file.

    Joe Liske